1. Field of the Invention
The present invention pertains to the design of electrodes for applications such as in the field of acousto-optics and pertains particularly to an electrode that has a balanced centroid, soft edges and an apodization ratio greater than one.
2. Related Information
Acousto-optic (AO) devices are based on the photoelastic effect of certain crystals. The crystals are designed so that sound waves change the optical properties of the crystals. Sound waves are injected into a crystal typically using piezo-electric transducers. As the crystal propagates the sound waves, areas of compression and rarefraction change the optical properties of the crystal. Light transmitted through the crystal is then deflected modulated and/or frequency shifted as the light travels through the crystals. Changes in the optical properties of the crystal result from the change in index of refraction caused by the strain produced by the sound waves. For a good general discussion of acousto-optic devices, see Akis P. Goutzoulis, Dennis R. Pape, Design and Fabrication of Acousto-Optic Devices, Marcel Dekker, Inc., New York, N.Y., 1994.
Piezo-electric transducers are formed by placing piezo-electric materials between a top electrode and a bottom electrode. Multiple electrodes can be used to create multi-channel devices. In some designs it is desirable to nest an array of electrodes to produce overlapping sound fields. Such arrays of electrodes are often composed of apodized electrodes. An apodized electrode is an electrode whose height varies over the interaction length of the electrode. The apodization ratio of an electrode is the maximum height of the electrode divided by the minimum height of the electrode.
When used in acousto-optical applications, it is generally the rule that light encounters an acousto-optical crystal traveling in a direction parallel to the interaction length of an electrode, and perpendicular to the height of the electrode. The centroid of an electrode is the center of mass of the electrode.
In the prior art, apodized electrodes have been developed so that the area centroid of the electrode occurs at the midpoint of the interaction length of the electrode. However in order to achieve this, such prior-art electrodes have a shape that is basically the sum of two primitive shapes, typically two trapezoids. When two trapezoids are joined together to form a common shape, the slope of the edge of the common shape at the intersection point of the two trapezoids is discontinuous.